What the Zoom Lens Crop Factor Calculator does
This calculator converts a lens's focal length and aperture to their full-frame equivalents on APS-C, Micro Four Thirds, 1-inch, phone and medium-format sensors, gives the horizontal, vertical and diagonal angle of view, and compares two camera setups - including the focal length the second camera needs to see the same view as the first.
Crop factor is the ratio of a full-frame sensor's diagonal (43.27 mm) to your sensor's diagonal. A smaller sensor records only the middle of the image a lens projects, so the same lens frames more tightly, as if it were longer. Multiplying by the crop factor translates a focal length into the language most photographers think in - "a 50 mm on APS-C looks like a 75 mm" - and does the same for depth of field.
How to use it
- Choose your sensor format. Sizes for common formats are filled in; choose Custom to enter your camera's exact width and height from its specification sheet.
- Enter the focal length marked on the lens and, optionally, its f-number.
- Phone cameras usually quote a "24 mm" or "26 mm" that is already a full-frame equivalent. Tick the box under the focal length and the calculator works out the real focal length instead.
- Read the equivalent focal length and aperture at the top, then the angle of view and the to-scale drawing of your sensor inside a full-frame outline.
- Open "Compare with a second camera" to put two setups side by side and see the focal length and aperture the second camera needs to match the first.
Reading the results
The equivalent focal length describes framing only. The lens is unchanged: a 50 mm lens on any camera still magnifies the subject the same amount; the smaller sensor simply crops the edges away.
The equivalent aperture describes depth of field and the total light gathered for the same framing. Exposure does not change - f/1.8 is f/1.8 on any sensor for shutter speed and ISO - but a 50 mm f/1.8 on APS-C gives roughly the background blur of a 77 mm f/2.8 on full frame.
Angle of view is measured across the width, the height or the diagonal. Lens makers usually quote the diagonal; the horizontal figure is the one that matters for a landscape or a room.
When two sensors have different shapes (3:2 against 4:3, for example), matching the diagonal and matching the width give slightly different focal lengths, and the comparison shows both.
Worked example: a 50 mm f/1.8 lens on a Nikon, Sony or Fujifilm APS-C camera
The sensor is about 23.5 x 15.6 mm, so its diagonal is sqrt(23.5^2 + 15.6^2) = 28.21 mm.
The crop factor is 43.27 / 28.21 = 1.53, usually rounded to 1.5.
The equivalent focal length is 50 x 1.53 = 76.7 mm, and the equivalent aperture for depth of field is 1.8 x 1.53 = f/2.8.
The diagonal angle of view is 2 x atan(28.21 / (2 x 50)) = 31.5 degrees and the horizontal angle 2 x atan(23.5 / 100) = 26.4 degrees. A 25 mm lens on Micro Four Thirds (crop 2.0) gives almost exactly the framing of a 50 mm on full frame.
Formulas and scoring rules
- Crop factor
crop = 43.2666 / sqrt(width^2 + height^2)43.2666 mm is the diagonal of a 36 x 24 mm full-frame sensor.- Equivalent focal length
f_equivalent = f x crop- Real focal length from a quoted equivalent
f = f_equivalent / crop- Equivalent aperture (depth of field, total light)
N_equivalent = N x crop- Angle of view
angle = 2 x atan(d / (2 x f)), d = sensor width, height or diagonalFor a rectilinear lens focused at infinity; close focusing and fisheye lenses differ. Angles are shown to 0.1 degree and focal lengths to 0.1 mm.- Light gathered relative to full frame
stops = log2(864 / (width x height))864 mm^2 is the full-frame area.
Why phone cameras quote equivalent focal lengths
A phone's main camera lens is typically about 6 to 7 mm long. Quoting that number would mean nothing to most people, so manufacturers quote the full-frame equivalent instead - 24 mm, 26 mm, 77 mm for a telephoto. With the box ticked, this calculator reverses the conversion: a "24 mm" main camera on a 1/1.28-inch type sensor (crop about 3.4) is really a 7 mm lens, and its f/1.8 aperture behaves like about f/6.2 on full frame for depth of field, which is why phones use software to imitate background blur.
The "inch" sizes in phone and compact sensor names come from old video camera tubes and are not a measurement: a 1-inch type sensor is about 16 mm across the diagonal. That is why this page works from the width and height in millimetres.
Limitations: what the result does not prove
- Sensor sizes in the list are typical. Models differ by a few tenths of a millimetre, so the crop factor is accurate to about 1-2% unless you enter your camera's exact dimensions.
- Angles assume a rectilinear lens focused at infinity. At close focus, lenses that breathe change their angle of view, and fisheye lenses follow a different projection.
- Phones crop the sensor for some aspect ratios and video modes, and stabilisation crops further. The quoted equivalent may refer to the photo mode only.
- Equivalence ignores sensor technology, noise processing and lens sharpness. It compares geometry, not image quality.
Privacy: where your data goes
Everything you paste, type or drop is processed in this browser tab. It is not uploaded, logged, stored or sent to analytics. Session recording and tag-manager scripts are switched off on this page.
Standards and sources
- Micro Four Thirds system standard (sensor size and mount)
- Image sensor format - table of sensor dimensions
- CIPA (Camera and Imaging Products Association) standards
Frequently asked questions
What is the crop factor of an APS-C sensor?
About 1.5 for Nikon, Sony and Fujifilm APS-C (23.5 x 15.6 mm) and about 1.6 for Canon APS-C (22.3 x 14.9 mm). Micro Four Thirds is 2.0, a 1-inch type sensor about 2.7, and 44 x 33 mm medium format about 0.79.
What is 50mm on APS-C equivalent to on full frame?
About 75 to 77 mm on Nikon, Sony and Fujifilm bodies (crop 1.53) and 80 mm on Canon APS-C (crop 1.6). It frames like a short portrait telephoto, which is why a 35 mm lens is the usual "normal" lens on APS-C.
Does crop factor change the aperture?
Not for exposure: f/2 lets through the same light per unit area on any sensor, so shutter speed and ISO are unchanged. For depth of field and total light at the same framing, multiply the f-number by the crop factor - f/2 on Micro Four Thirds looks like f/4 on full frame.
How do I convert a phone camera's focal length?
Phones usually quote the full-frame equivalent already. Choose the phone's sensor size, enter the quoted figure and tick "already a full-frame equivalent" to get the real focal length; a 24 mm-equivalent main camera on a 1/1.28-inch sensor is about 7 mm.
How do I calculate the angle of view of a lens?
Use 2 x atan(d / 2f), where d is the sensor width, height or diagonal and f the focal length. A 24 mm lens on full frame covers 84 degrees diagonally and 74 degrees horizontally. The calculator shows all three angles for any sensor.
What lens gives the same view on Micro Four Thirds as 50mm on full frame?
A 25 mm lens, because the Micro Four Thirds crop factor is 2.0. Open the comparison section to work this out for any pair of cameras; it also shows when the sensors' different shapes make width and diagonal disagree.
Last reviewed by the A2Z.Tools team against the sources listed above.
